1. Technical Field
The present invention relates to an ink composition for ink jet recording, a penetrant for ink jet recording, and a recording apparatus.
2. Related Art
Recently, an ink jet recording method has been widely used in which small ink droplets are ejected from nozzles of an ink jet recording head onto a recording medium such as plain paper or glossy paper to form an image or a character thereon. It is desired that high-quality printing be performed at a high speed on, in particular, plain paper (for example, PPC paper or printing uncoated paper) which is cheap and readily available. However, when an aqueous ink is used for performing printing on plain paper, curling and cockling after printing are large problems to solve. In addition, when an aqueous ink is used for forming a photographic image on dedicated glossy paper, the graininess, glossiness, and wear resistance of the formed image have a tendency to deteriorate.
In order to solve such problems, a technique of adding a water-soluble organic solvent such as 1,2-alkanediol or a glycol ether to an aqueous ink is disclosed (refer to JP-A-2007-153975). According to such a technique, when printing is performed on plain paper, curling characteristics are superior and plural satellite dots are ejected along with main dots. Therefore, when printing is performed on dedicated glossy paper, an image having satisfactory graininess, glossiness, and wear resistance can be formed thereon.
In addition, a technique of adding a nonionic surfactant represented by a formula of R—[(PO)m-(EO)n—H]x (wherein R represents a X-valent hydrocarbon group having 4 to 30 carbon atoms; PO represents a propylene oxy group; EO represents an ethylene oxy group; m represents an integer of 0 to 10; n represents an integer of 10 to 30; and x represents an integer of 1 to 3) to an aqueous ink, is disclosed (refer to JP-A-2005-82663). According to such a technique, an image having superior glossiness can be formed on various recording mediums.
Incidentally, in recent years, various countermeasures have been studied in order to suppress the emission of volatile organic compounds (VOC) which have a concern of adversely affecting people's health. VOC is a collective term for organic compounds which have volatility and are gaseous in the atmosphere. VOC includes 1,2-hexanediol and triethylene glycol monobutyl ether which are added to an aqueous ink in the related art. Therefore, the development of a material, which can be used instead of these water-soluble organic solvents, has been desired. However, it is significantly difficult to obtain the same level of performance as that of the aqueous inks described above in JP-A-2007-153975 and JP-A-2005-82663 while reducing the total VOC emission of an aqueous ink.
In the mean time, the aqueous ink described in JP-A-2007-153975, to which, for example, 1,2-alkanediol or a glycol ether is added, may have attacking properties of changing or deforming members included in an ink jet head. Therefore, the reliability of an ink jet head is impaired after a long period of use and thus there are cases where a satisfactory image cannot be obtained.
In addition, the nonionic surfactant (penetrant), which is described as an example in JP-A-2005-82663, is a material having a propylene oxy group. When such a material is added to an aqueous ink, the clouding point of the entire aqueous ink is reduced and thus there are cases in which the aqueous ink becomes cloudy according to the usage environment, which causes a problem in terms of storage stability. The present inventors found that, in order to solve such a problem, it is effective that an anionic surfactant is further added to the aqueous ink to increase the clouding point of the entire aqueous ink. However, when an anionic surfactant is added, the bubble-foaming properties of the aqueous ink are increased and generated bubbles are difficult to remove. Therefore, it is difficult to use this aqueous ink in practice.